Thesis

Key Genes Governing Odor-Mediated Paralysis in a Nematode Share a Pathway with an Ancient Nematocide

Within the last decade, nematode species other than Caenorhabditis elegans (C. elegans) have been studied intensively in the realm of developmental biology. One particular field of interest in studying these satellite model organisms is insect-nematode interaction. These interactions are governed via olfaction of volatile compounds, but the mechanisms underlying the biological function remains unknown. Given that C. elegans does not have a known host organism, we turn our focus to the nematode, Pristionchus pacificus), an emerging satellite model organism, to study this insect-nematode interaction. P. pacificus are associated with several beetle species, including the oriental beetle, which produces the pheromone: Z-7-tetradecen-2-one (ZTDO). Although ZTDO attracts P. pacificus, ZTDO also paralyzes P. pacificus during specific larval stages. OBI-1 was identified as a protein that regulates response to ZTDO and a mutation in obi-1 induces stage-specific ZTDO paralysis. To investigate the pathway in which ZTDO affects obi-1 mutants, we isolated three mutant candidates from a forward genetic screen using ethyl methanesulfonate (EMS) that exhibit partial suppression of ZTDO hypersensitivity in the J4 developmental stage: csu61, csu63, and csu64. Additionally, these genetic suppressors can suppress hypersensitivity to betaine - a potent nematocide - suggesting overlap between chemosensory pathways. We detected candidate mutations in genes using whole genome sequencing, bulk segregate mapping, and double mutant analysis. Specifically, we identified two mutant alleles in a novel gene on Chromosome X in two different suppressor mutants, suggesting saturation of our forward screening method. Ultimately, the understanding of P. pacificus host interactions and the pathways that govern them may act as a bridge for understanding the role olfaction has played in the evolution of parasitism.

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